Recently, in the field of magnetic recording, with the improvement in performance of recording and reproducing equipment such as digitalization, scale reduction, and elongation of time for use, a high-density magnetic recording medium suitable therefor has been developed actively. Recently, a metal thin film type magnetic recording medium, which is extremely advantageous for a short wavelength recording, is put into practical use in lieu of an application type magnetic recording medium. The metal thin film type magnetic recording medium is generally referred to a tape or a disk, wherein a magnetic layer of a ferromagnetic metal thin film is formed as a recording layer on a non-magnetic base (or a non-magnetic support). Systems for recording information on and reproducing information from the high-density magnetic recording medium include a digital video deck and a hard disk drive.
The magnetic layer of the metal thin film type magnetic recording medium such as a digital video tape has an extremely good surface property, i.e. a small roughness on the surface. For this reason, a contact area between the magnetic layer and a magnetic head is larger, whereby the magnetic layer is liable to be abraded by receiving a great friction force while being in a rapid sliding movement with the magnetic head during a process of recording/reproducing signals. Abrasion of the magnetic layer greatly affects the running durability, the still durability, or the like, so that reduction of the abrasion of the magnetic layer is an important object in the research and development of the metal thin film type magnetic recording medium.
In this situation, an attempt is made to reduce the abrasion by disposing a protective film and a lubricant layer on a surface of the magnetic layer in this order to improve the running durability and the still durability. In the case where the lubricant layer is disposed, the protective film and the lubricant layer on the magnetic layer surface are required to be thin in order to prevent the output reduction caused by a spacing loss between the magnetic recording medium and the magnetic head as much as possible for achieving a high output. Particularly, the lubricant layer is required to exhibit a lubricating property with a thickness as small as several nanometers.
Further, in a typical hard disk drive, a contact start stop (CSS) mode is employed. The “CSS” mode refers to a mode wherein a magnetic head contacts with the disk when a hard disk that is a high-density magnetic recording medium stops, and the magnetic head is floated by an air stream which is caused by a rapid rotation of the hard disk when the drive starts, and recordation and reproduction of information is carried out with the floated magnetic head. When the drive stops, the rotation speed of the disk is reduced and the magnetic head contacts with the hard disk again.
In this CSS mode, the magnetic head runs scrubbing the surface of the hard disk at the time of starting and stopping, which causes friction force that may give a serious problem. It is required that the friction coefficient of the recording medium which has been subjected to a CSS running test is the same as the initial friction coefficient in order to maintain reliability of the hard disk drive. However, it is difficult to meet this requirement for the magnetic disk wherein a surface flatness is high, that is, roughness is small. Further, a problem of “head crash” should be resolved. The “head crash” is collision between the head and the medium during the high speed rotation of the hard disk. One factor of the head clash is that the magnetic recording medium does not have appropriate protective film and lubricant layer.
In this situation, use of lubricants suitable for a magnetic recording medium is widely studied. One of the lubricants is a fluorine-based compound. Since the fluorine-based compound exhibits an excellent lubricating property, use of various compounds is proposed (see Japanese Kokai (Laid-Open) Publication Nos. 2002-92858, 2002-150530(A), 2002-241349(A) and 5-194970/1993(A).
However, the lubricating property of the lubricant used for the magnetic recording medium is required to be further improved in order to adapt to new technologies such as an MR head or a GMR head and a contact recording mode, which technologies are entailed by a higher recording density.
The property which is required for a lubricant used for a magnetic recording medium is: exhibiting superior lubricating property when used under a low-temperature environment; the ability of being applied into a thin film with the lubricating property maintained; maintaining the lubricating property under long-term use; and exhibiting a small powder deposition on a magnetic head. Herein, “powder deposition” means that the lubricant is scraped off during the running of the medium in contact with the magnetic head and the scraped powder deposits on the magnetic head.
These requirements need to be satisfied at a very high level because of the property of the magnetic recording medium. Therefore, the conventional lubricants are difficult to satisfy all these requirements.
In view of the aforementioned situations, the object of the present invention is to provide a lubricant that exhibits excellent lubricity under various use conditions and maintains lubricating effect even if it is subjected to long-time use and gives a magnetic recording medium which exhibits a small powder deposition when the lubricant forms a lubricant layer of the magnetic recording medium, and to provide the magnetic recording medium wherein the lubricant is used and the production method of the magnetic recording medium.